Most landfill gas is produced by biodegradation, which occurs when organic waste is broken down by bacteria naturally present in the waste and in the soil used to cover the landfill. Landfill gas is mostly made of methane, carbon dioxide, and trace amount of a wide variety of volatile organic compounds.
Landfill gases can contribute to ozone formation, atmospheric photochemical reaction, and other types of air pollution. Landfill gases can also create dangerous conditions. For example, if methane is present in the air at higher concentrations, it can be explosive. Landfill gases may also contribute to water pollution if it migrates and comes in contact with groundwater. Therefore, it is desirable to collect landfill gas to prevent these dangers. Collected landfill gases can be used as a source of power generation, or be incinerated before being released into the atmosphere.
Landfill sites can sometimes be filled with liquid. Excessive levels of liquid can reduce gas extraction efficiency drastically. In order to ensure efficient extraction of landfill gases, such liquid needs to be pumped out of the landfill site.